Communication apparatus and communication method for multi-ap joint transmission

ABSTRACT

An access point (AP) includes circuitry, which, in operation, generates a frame that includes joint transmission (JT) data and a JT identity that uniquely identifies the JT data. The access point further includes a transmitter, which, in operation, transmits the frame to one or more APs that jointly transmit the JT data to a communication apparatus.

BACKGROUND 1. Technical Field

The present disclosure generally relates to communication apparatus andmethods for electronic devices and systems, and more particularlyrelates to joint transmission in multi-AP networks.

2. Description of Related Art

Wireless networks that communicate via multi-AP joint transmissionenable electronic devices to communication in networks with jointtransmissions sent to multiple electronic devices. Such networks haveadvantages over other wireless networks in which wireless communicationis limited to a single transmission to one electronic device.

SUMMARY

One non-limiting and exemplary embodiment facilitates providing jointtransmission communication in multi-AP networks. By way of example, thiscommunication includes joint transmission from two or more of an accesspoint (AP) to one or more wireless station (STA).

In one general aspect, the techniques disclosed here feature an accesspoint (AP). The access point includes circuitry, which, in operation,generates a frame including joint transmission (JT) data and a JTidentity that uniquely identifies the JT data; and a transmitter, which,in operation, transmits the frame to one or more other APs that jointlytransmit the JT data to a communication apparatus.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to illustrate variousembodiments and to explain various principles and advantages inaccordance with present embodiments.

FIG. 1 is a wireless network with a multi-AP system in accordance withan example embodiment.

FIG. 2A is a multi-AP system shown as an enterprise network inaccordance with an example embodiment.

FIG. 2B is a multi-AP system shown as a home or office network inaccordance with an example embodiment.

FIG. 2C is a multi-AP system shown as a Master-Slave configuration inaccordance with an example embodiment.

FIG. 3 is MAC Protocol Data Unit (MPDU) in accordance with an exampleembodiment.

FIG. 4 is a message sequence in Joint Transmission in a multi-AP systemin accordance with an example embodiment.

FIGS. 5A and 5B are Data frames used to encapsulate JT Data inaccordance with an example embodiment.

FIG. 6 shows a data frame, a first table showing protocol names andpayload types, and a second table showing AP coordination packet type inaccordance with an example embodiment.

FIG. 7 shows joint transmission between a Master AP, Slave APs, and aTarget STA in accordance with an example embodiment.

FIG. 8 is a JT Trigger frame in accordance with an example embodiment.

FIG. 9 is a message sequence for a Joint Transmission Session between aMaster AP and Slave APs in a multi-AP system in accordance with anexample embodiment.

FIG. 10 shows AP Coordination Action frames exchanged over the air tonegotiate or tear down a Joint Transmission Session in accordance withan example embodiment.

FIG. 11 shows a frame in which an Ethernet Frame encapsulates JT Data aswell AP Coordination Action frames in accordance with an exampleembodiment.

FIG. 12 shows a Trigger frame for Joint Transmission to a Target STA inaccordance with an example embodiment.

FIG. 13 shows a communication exchange in which the Master AP does notparticipate in the Joint Transmission in accordance with an exampleembodiment.

FIG. 14 shows Action Frames used by AP in the information query phase togather information from another AP in accordance with an exampleembodiment.

FIG. 15 shows a frame for data sharing from the Master AP to Slave APsin accordance with an example embodiment.

FIG. 16 shows a JT Data frame as an Aggregated MAC Protocol Data Unit(A-MPDU) in accordance with an example embodiment.

FIG. 17 shows a frame as an Aggregated MAC Protocol Data Unit (A-MPDU)used for data sharing to Slave APs in accordance with an exampleembodiment.

FIG. 18 shows a Joint Transmission Trigger frame in accordance with anexample embodiment.

FIG. 19 is example of Distributed MU-MIMO Joint Transmission to two STAsthat are both associated with the Master AP in accordance with anexample embodiment.

FIG. 20 is an example of an electronic device in accordance with anexample embodiment.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendepicted to scale.

DETAILED DESCRIPTION

Electronic devices can be configured to transmit and receive jointtransmission (JT) data in multi-AP networks. These electronic deviceshave many advantages over conventional electronic devices that arelimited to single transmissions to a single electronic device.Performing joint transmissions in multi-AP networks, however, hasnumerous technical problems.

Existing 802.11 BSSs (Basic Service Sets) operate as a standalone unit.The APs of each BSS provide wireless communication service only to thewireless stations (STA) that are associated with the respective APs. Thedata rate that the AP can provide for the wireless link to an associatedSTA depends on the MCS (modulation and coding scheme) used for the link,which in turn depends on the SINR (signal-to-interference-plus-noiseratio) of each STA. Typically higher MCS can be achieved at higher SINR,while only a low MCS may be possible at low levels of SINR. In astandalone BSS, while the signal ratio may be controlled by the AP byadjusting the Transmit Power, the interference experience by a STA ismuch more difficult to control. This problem is especially true for STAsthat exist at the edge of a network and that are within the wirelessrange of multiple BSSs (also known as the OBSS (Overlapping BSS) zone).A useful signal in one BSS is essentially interference for the STAs ofanother BSS.

Multi-AP coordination (e.g., coordination among the APs of neighboringBSSs) can be used as an effective way for improving the SINR of memberSTAs. Such schemes are made possible by the proliferation of APs, suchas dense AP deployment in a managed network (e.g. enterprise network,stadium settings, etc.) or in-home networks (e.g., with multi-AP homemesh networks).

The various multi-AP coordination schemes can may be divided into twogeneral groups. The first group includes schemes that attempt to reducethe interference to OBSS through Transmit power control, coordinatedbeamforming, coordinated Null-forming, coordinated scheduling, etc. Thesecond group includes schemes that attempt to increase the signal levelat a STA through synchronized transmission by multiple APs to the sameSTA. Schemes of the second group may be known as Multi-AP JointProcessing or Multi-AP Joint Transmission, or Distributed MU-MIMO.

Joint Transmission not only improves the signal level, but alsodecreases interference by converting the interfering signal to desiredsignal. Example embodiments thus solve technical problems associatedwith STAs in overlapping BSSs or multi-AP systems by reducinginterference to the STAs and improving SINR to the STAs. These problemsinclude how to distribute and synchronize Joint Transmission Data (JointMU-MIMO Data) among Slave APs and other problems discussed herein.

Example embodiments include apparatus and methods that transmit andreceive joint transmissions in multi-AP networks. Such apparatus andmethods include electronic devices with transmitters and/or receivers,such as APs and STAs. One example embodiment is an AP that includescircuitry, which, in operation, generates a frame, a frame body of theframe includes joint transmission (JT) data and a JT identity thatuniquely identifies the JT data; and a transmitter, which, in operation,transmits the frame to one or more APs that jointly transmit the JT datato a communication apparatus.

Another example embodiment is an access point (AP) that includes areceiver, which, in operation, receives from an AP a frame that includesJoint Transmission (JT) data and a JT identity that uniquely identifiesthe JT data; and local memory that stores the JT data and the JTidentity.

Another example embodiment is a communication method in which one ormore access points (APs) jointly transmit to a communication apparatus.The method includes, the method comprising transmitting, from a first APand to one or more second APs, a frame in which a frame body of theframe includes joint transmission (JT) data and a JT identity thatuniquely identifies the JT data; and transmitting, from the one or moresecond APs, the JT data jointly to the communication apparatus.

FIG. 1 is a wireless network with a multi-AP system 100 in accordancewith an example embodiment. By way of example, the system 100 includesthree BSSs (shown as BSS1, BSS2, and BSS3). Each BSS has at least one AP(shown as AP1, AP2, and AP2). A plurality of STAs (shown as STA1-STA5)are distributed throughout the system. STA1 exists in a single BSS(BSS1); STA2 exists in three overlapping BSSs (BSS1-BSS3); STA3 existsin two overlapping BSSs (BSS1 and BSS3); STA4 exists in two overlappingBSSs (BSS2 and BSS3); and STA5 exists in a single BSS (BSS2).

In the FIG. 1, although STA2 is associated with AP3, the three APs (AP1,AP2 and AP3) may coordinate their transmission to simultaneouslytransmit to STA2. This simultaneous transmission increases the SINRlevel at STA2 and facilitates the use of higher MCS which translates tohigher throughput for STA2.

Although Multi-AP Coordination schemes typically utilize some sort oftime synchronization among the participating APs, the level ofsynchronization utilized is highest for Joint Transmission, especiallyfor Distributed MU-MIMO. Due to this, one or more example embodimentsimplement Joint Transmission in which one AP (called the Master AP)provides the synchronization signal and the other participating APs(called Slave APs) are in range of the Master AP. In FIG. 1, AP3 wouldbe the Master AP while AP1 and AP2 are Slave APs. The Master AP may alsobe known by alternate names such as Coordinating AP, or JointTransmission (JT) AP, or a multi-AP Controller etc., while the Slave APmay also be known as multi-AP device, or coordinated AP, etc.

In an example embodiment and as discussed in more detail below, JointTransmission includes all participating APs to transmit the same signalto the STA. This includes the MAC layer specific fields be equivalentwith all participating APs.

FIG. 2A is a multi-AP system 200 shown as an enterprise network inaccordance with an example embodiment. By way of example, the systemincludes multiple APs (shown as AP1-AP8) broadcasting with overlappingtransmissions. Each AP operates a respective channel (Ch), such as AP1at Ch 36, AP2 at Ch 52, AP3 at Ch 149, AP4 at Ch 44, APS at Ch 56, AP6at Ch 161, AP7 at Ch 48, and AP8 at Ch 60.

In enterprise networks, APs position and frequency allocation arecarefully planned during deployment to maximize capacity. As shown inFIG. 2A, adjacent APs use non-overlapping channels to minimize inter-BSSinterference. APs can use high gain directional antennas with narrowbeam width. Adjacent APs may not be in wireless range of each other.Multiple APs or all APs can use the same Service Set Identifier (SSID).Further, APs are connected using Ethernet and may be configured and/orcontrolled by a central AP Controller. Most edge STAs would be withincoverage of at least two APs. AP to AP communication can use, forexample, Ethernet or out-of-band Mesh wireless direct links. Even thoughneighboring APs are allocated non-overlapping primary channels, whenwide-band channels are used it is inevitable that inter-BSS interferencewill be present in the OBSS zones. Since most enterprise networks arecentrally managed and coordination among APs is easier and henceenterprise networks are a prime candidate for a Joint Transmissionsystems.

FIG. 2B is a multi-AP system 230 shown as a home or office network inaccordance with an example embodiment. By way of example, the systemincludes multiple APs (shown as AP1-AP3) broadcasting with overlappingtransmissions. Each AP operates a respective channel, such as AP1 at Ch36, AP2 at Ch 149, and AP3 at Ch 52.

Multi-AP systems (e.g. Wi-Fi EasyMesh) is an example configuration toprovide Wi-Fi coverage across an entire area, such as a house or office.AP position and frequency allocation are planned to maximize coverage.For example, one AP may act as a Multi-AP controller while the rest ofthe APs act as Multi-AP agents. APs can be expected to be in wirelesscoverage of at least one other AP. A Backhaul BSS is setup for AP to APsignaling. The Backhaul BSS may use a different SSID from the fronthaulSSID. Most edge STAs would be within coverage of at least two APs.Furthermore, AP to AP communication can use wireless direct links or amix of wireless and wired links. Such multi-AP home or small officenetworks are also a good candidate for a Joint Transmission systems.

FIG. 2C is a multi-AP system 260 shown as a Master-Slave configurationin accordance with an example embodiment. By way of example, the systemincludes a Master AP 270, two Slave APs 280 and 282, and a STA 284. APto AP communication occurs over links 290, and communication between APsand the STA occurs over links 292.

For Joint Transmission, the APs possess the transmission data (upperlayer data) that is to be jointly transmitted to a STA prior to theactual Joint Transmission. In one or more example embodiments, however,possessing the transmission data may not be enough in order to realizethe SINR gains of Joint Transmission. The actual data symbols that aretransmitted on the air need to be synchronized among the participatingAPs, such as multiple APs or all APs. This means that the PHY layer andMAC layer processing of the transmission data are the same among theparticipating APs. Example embodiments include systems, apparatus, andmethods to distribute and synchronize the data for Multi-AP JointTransmission.

In one or more example embodiments, Joint Transmission takes place intwo phases: Distribution of JT data to Slave APs and Joint Transmissionto the Target STA.

In the first phase (Distribution of Joint Transmission Data to SlaveAPs), the data to be jointly transmitted is distributed to theparticipating Slave APs prior to the actual joint transmission over theAP to AP link, such as link 290 in FIG. 2C. The distribution may takeplace over the wireless backhaul link between the APs, or it may alsohappen over wired backhaul link between the APs, e.g., Ethernet. Whenwireless backhaul is used, prior to initiating Joint transmission, theSlave APs may have associated with the Master AP on a separate BSS setupby the Master AP for the purpose of communication among the APs. Thewireless channel used for the backhaul link among APs may be differentfrom the fronthaul link between the APs and the Target STA.

In the second phase (Joint Transmission to the Target STA), actual jointtransmission by two or more participating APs to the Target STA occursover a link, such as wireless links 292 in FIG. 2C. The jointtransmission may be preceded by a synchronization signal from the MasterAP over the link 290, which may be called the Slave Trigger frame or theJoint Transmission (JT) Trigger frame. In some scenarios, the Master APmay also participate in the joint transmission while in some scenariosthe Master AP may not take part in the joint transmission but only theSlave APs may participate. Different Sets of APs may be involved injoint transmissions to different Target STAs.

FIG. 3 is MAC Protocol Data Unit (MPDU) 300 to be jointly transmitted inaccordance with an example embodiment. The MPDU includes a MAC Headerand a Frame Body. The MAC Header includes Frame Control, Duration,Address 1 (Receiver Address), Address 2 (Transmitter Address), Address 3(BSSID), Sequence Control, QoS Control, and HT Control. The Frame Bodyincludes Data Payload, MIC, and FCS. The Address 3 field carries theBSSID if the Data frame carries an A-MSDU, otherwise the Address 3 fieldcarries the Source Address (SA) i.e. the MAC address of the device thatis the source of the Data payload.

In order to realize the SINR gains of Joint Transmission, the actualdata symbols that are transmitted on the air are synchronized among theparticipating APs. Further, the PHY layer and MAC layer processing ofthe transmission are the same among the participating APs. Typically,for normal transmissions (e.g., non-joint transmissions), the upperlayer (e.g., IP layer) passes the data payload (e.g., IP packets) to betransmitted to the MAC layer which performs the MAC layer processing,such as pre-pending the MAC headers, adding FCS, MAC padding ifrequired, etc. to create the MPDU (MAC Protocol Data Unit) 300. Ifprotection is enabled, the data payload may be further subjected toencryption procedure which results in the addition of the CCMP Headerfield and the MIC fields to the MAC frame body. The MPDU is then passeddown to the PHY layer for PHY layer processing such as pre-pending thePHY preamble, applying PHY encodings, adding PHY padding etc. to createthe PPDU (PHY Protocol Data Unit) and finally transmitting the PPDU outon the air.

For Joint Transmission, participating APs need to be aware of the MACand PHY parameters to be applied to the data payload. In addition, atthe MAC layer, there are several fields that are locally generated.While some fields like Frame Control, Address 2 (TA), Address 3 (BSSID),QoS Control, HT Control may be overwritten by the MAC layers of theSlave APs to match the fields generated by the Master APs, some fieldslike Sequence Control, CCMP Header are different for each MPDU and aretypically generated locally at each AP; hence such fields are moredifficult to synchronize among the APs. In addition, more than one MPDUmay also be aggregated at the MAC layer to form the A-MPDU (AggregatedMPDU), or one MPDU may constitute a S-MPDU (Single MPDU). In order tosynchronize the data to be jointly transmitted among the MAC layers ofall participating APs, the Master AP may generate and distribute theactual MAC layer A-MPDU or S-MPDU to all the participating Slave APs.The Sequence Control field in the MPDUs are also generated by the MasterAP and the same number space is used for the Sequence Number sub-fieldof the Sequence Control field for both direct transmission (i.e. sing APtransmission) from the Master AP to the Target STA as well as for jointtransmissions. If encryption is enabled, the Master AP also encrypts theData payload and appends the MIC field. In this case, the JointTransmission (JT) Data refers to the MAC layer data that is to bejointly transmitted.

In some cases, the Master AP may not be involved in the actual jointtransmission phase (e.g., only the Slave APs may participate in thejoint transmission). This may happen when the Master AP is implementedas a central controller and is far from the Target STA. In this case,the Target STA would be associated with one of the Slave APs and not theMaster AP.

In such cases where the Target STA is associated with a Slave AP, duringthe data distribution phase, the Master AP sets the MAC header fields ofMPDU 300 such that the MPDU appears to be generated by the Slave AP withwhich the Target STA is associated, e.g., the Address 2 (TA) field andAddress 3 (BSSID) are set to the MAC address of the Slave AP. The MasterAP also queries the Slave AP for the next Sequence Control to be used,and optionally the CCMP Packet Number (PN) and encryption Key ID to beused for transmission to the Target STA and sets the fields of the MPDU300 respectively. The Sequence Control field in the MPDUs in this caseare generated by the Slave AP and the same number space is used for theSequence Number sub-field of the Sequence Control field for both directtransmission (i.e. sing AP transmission) from the Slave AP to the TargetSTA as well as for joint transmissions.

FIG. 4 is a message sequence 400 in Joint Transmission in a multi-APsystem in accordance with an example embodiment.

In a distributed wireless network, such as 802.11 WLANs, the access tothe wireless channel is controlled by CSMA/CA, and it is difficult topredict the exact transmission times. Similarly, transmission failuresand re-transmissions make it difficult to maintain the order oftransmission. Due to this, for Joint Transmissions, it may beadvantageous to de-couple the data distribution phase and the jointtransmission phase.

As shown in FIG. 4, Joint Transmission occurs in two phases:Distribution of Joint Transmission data to Slave APs and JointTransmission to one or more Target STAs. In the first phase, one or moreJoint Transmission Data are distributed to Slave APs (e.g., over awireless backhaul). Each Joint Transmission Data is assigned a uniqueID. In the second phase, the Master AP initiates the Joint Transmissionby transmitting the JT Trigger frame. This frame carries the Unique IDthat identifies the Joint Transmission Data to be jointly transmitted byall participating APs.

FIG. 4 shows an example message sequence involved in a jointtransmission in which the data distribution phase 410 is de-coupled fromthe joint transmission phase 420. During the data distribution phase410, the Master AP distributes one or more Joint Transmission (JT) Datato the Slave APs. The JT Data in this case may be the actual S-MPDU orA-MPDU to be jointly transmitted and is encapsulated in another Dataframe addressed to the Slave APs. To reduce the overhead of distributingthe JT Data, the encapsulating Data frame may be transmitted to SlaveAPs as groupcast transmission instead of unicast transmissions. TheMaster AP may also use Multi-user (MU) PPDU format to simultaneouslydistribute different JT Data to different Slave APs.

In order to uniquely identify each JT Data, the Master AP also assigns aunique ID which may be called a JT Packet ID, to each JT Data. EachSlave AP, upon receiving the encapsulated JT Data, de-encapsulates andsaves the JT Data in local memory indexed by the JT Packet ID. To ensurethat the Slave AP saves the JT Data instead of forwarding it immediatelyto the Target STA, the data frame that encapsulates the JT Data can beaddressed to the Slave AP by setting the RA to the MAC address of theSlave AP. If the four-address MAC Header is used for the Data frame toSlave APs, both the RA (Address 1) and DA (Address 3) can be set to theSlave AP's MAC address. Due to the stringent time synchronizationrequirement for Joint Transmission and for faster retrieval, the JT Dataframe may be saved in a separate memory (e.g., different from the localEDCA queues).

In the Joint Transmission phase 420, the Master AP initiates the Jointtransmission by transmitting the JT Trigger frame to the Slave APs. TheJT Trigger frames provide time synchronization to the Slave APs. Inaddition, the JT Trigger frame also carries the JT Packet ID of the JTData to be jointly transmitted. Each Slave AP, upon receiving the JTTrigger frame, retrieves the JT Data from local memory corresponding tothe JT Packet ID and transmits the JT PPDU constructed from the JT Data.

FIGS. 5A and 5B are Data frames used to encapsulates JT Data inaccordance with an example embodiment.

FIG. 5A shows a Data frame 500 transmitted by the Master AP thatencapsulates JT Data, which in this case is an S-MPDU, within the framebody of the data frame 500. The S-MPDU is composed of a MPDU Delimiter,the actual MPDU and padding if required. A unique ID (JT Packet ID) isassigned to each Joint Transmission Data. In this case, the JT Packet IDuniquely identifies the S-MPDU.

FIG. 5B shows a Data frame 550 transmitted by the Master AP thatencapsulates JT Data, which in case is an A-MPDU, within the frame bodyof the data frame 550. The A-MPDU is composed of two or more A-MPDUsubframes, and EOF (End-of-frame) padding if required. Each A-MPDUsubframe shares the same format as an S-MPDU. In this case, the JTPacket ID uniquely identifies the A-MPDU.

If encryption is enabled, each of the MPDUs in the JT Data is alsoencrypted by the Master AP before encapsulating in the Data frame 500 or550.

Each Slave AP, upon receiving the encapsulated JT Data, de-encapsulatesand saves the JT Data in local memory indexed by the JT Packet ID. Dueto the stringent time synchronization requirement for JointTransmission, for faster retrieval the JT Data frame may be saved in aseparate memory (e.g., different from the local EDCA queues).

The Slave APs do not immediately forward the received JT Data to theTarget STA(s). To ensure this, if the four-address MAC Header is usedfor the Data frame to Slave APs, both the RA (Address 1) and DA (Address3) are set to the Slave AP's MAC address.

FIG. 6 shows a data frame 600, a first table 610 showing encoding of thepayload type field, and a second table 620 showing encoding of the APcoordination packet type field in accordance with an example embodiment.

The Data frame 600 encapsulates JT Data during the Data distributionphase (e.g., discussed at 410 in FIG. 4). In this example, the framebody of the data frame 600 carries an Ethertype 89-0d frame with thePayload Type field set to 5 “AP Coordination” to differentiate fromother encapsulation types. Ethertype 89-0d is the Ethertype originallyassigned for encapsulation of IEEE 802.11 frames within Ethernet frames.The Payload of the Ethertype 89-0d frame when the Payload Type is set to“AP Coordination” may carry the JT Data within the Packet Content fieldwhen the AP Coordination Packet Type field is set to 0, 1 or 2 asindicated in Table 620. The Destination MAC Address carries the MACAddress of the Target STA (e.g., target of the Joint Transmission). TheJT Packet ID is the unique ID assigned to the JT Data while the PacketLength field indicates the size of the JT Data carried in the PacketContent field. When 802.11 Data frames are exclusively used toencapsulate the JT Data, the Sequence Number subfield 630 in theSequence Control field 632 of the host 802.11 data frame may be used asan implicit JT Packet ID, and the JT Packet ID field may be omitted inthe Ethertype 89-0d frame body.

To ensure that the Slave APs save the JT Data instead of forwarding itimmediately to the Target STA, the data frame 600 that encapsulates theJT Data is addressed to the Slave AP by setting the RA field of the MACHeader to the MAC address of the Slave AP. If the four-address MACHeader is used, both the RA (Address 1) and DA (Address 3) are set tothe Slave AP's MAC address.

FIG. 7 shows joint transmission 700 between a Master AP, Slave APs, anda Target STA in accordance with an example embodiment.

In the Joint Transmission phase (e.g., discussed at 420 in FIG. 4), theMaster AP initiates the Joint transmission by transmitting the JTTrigger frame 710 to the Slave APs. In addition to PHY and MACparameters used for synchronization, the JT Trigger frame also carriesthe JT Packet ID of the JT Data to be jointly transmitted. Each SlaveAP's MAC layer, upon receiving the JT Trigger frame that identifies theSlave AP as a participating AP in the joint transmission, retrieves theJT Data from local memory corresponding to the JT Packet ID and passesdown to the PHY layer which constructs the JT PPDU from the JT Databefore transmitting its SIFS (Short Interframe Space) after the end ofthe JT Trigger frame. The Master AP too constructs the JT PPDU from theJT Data corresponding to the JT Packet ID and transmits the JT PPDU SIFS(Short Interframe Space) after the end of the JT Trigger frame. Sincethe channel states may be different at different APs, each Slave APs mayneed to consider the channel condition and transmit the JT PPDU only ifthe channel is considered idle during the SIFS after the end of the JTTrigger frame, except that NAV (Network Allocation Vector) set due toMaster AP's or Target STA's transmissions may be ignored. As for theTarget STA, upon receiving the JT Data, it may not even be aware thatmultiple APs were involved in the transmission. As far as the Target STAis concerned, this is just another transmission to it from the MasterAP, or the AP whose MAC Address appears in the TA address (Address 2)field of the frame. If the reception is successful, the Target STAproceeds to transmit the acknowledgement frame (ACK or Block Ack) to theAP whose MAC Address appears in the TA address (Address 2) field.

FIG. 8 is a JT Trigger frame 800 in accordance with an exampleembodiment. Each User Info field carries information of a set of SlaveAPs and Target STAs.

The MAC Address of Slave APs field identifies the Slave APsparticipating in the Joint Transmission for a particular set of STAs. Ifonly a single Slave AP is involved in the Joint Transmission, this maybe omitted and the Slave AP is identified by the RA field in the MACheader. The AID12 field within each user Info field may be set to aspecial value (e.g. 2047) to differentiate the JT Trigger frame from theother Trigger frames used to solicit uplink OFDMA transmissions.

The JT Packet ID field identifies the (stored) MPDUs to be carried inthe JT PPDU. In case of S-MPDU this may also be the value of theSequence Control field of the S-MPDU. The field value may be same fordifferent Slave APs if identical data is to be jointly transmitted(transmit diversity). Alternatively, the field value may be differentfor different Slave APs when different data are to be jointlytransmitted (D-MIMO).

In addition, the Joint Transmission PHY Layer Info specifies theadditional PHY parameters to be used for encoding of the JT PPDU. TheTarget STA Information carries information relevant for JointTransmission to one or more Target STAs by the Slave AP. The JointTransmission Information identifies the stored data to be transmittedand the spatial stream for the Target STA.

Further, the Spatial Stream Allocation field indicates the spatialstreams allocated for each Target STA and is only present in the case ofMIMO joint transmissions. The Starting Spatial Stream field indicate thefirst spatial stream allocated to the STA, while the Number of SpatialStreams field indicate the total number of consecutive spatial streams,including the first spatial stream, allocated to the STA.

FIG. 9 is a message sequence 900 for a Joint Transmission Sessionbetween a Master AP and Slave APs in a multi-AP system in accordancewith an example embodiment.

If the joint transmission is expected to take place for more than one ortwo frames, an example embodiment sets up a joint transmission sessionbetween the Master AP and the participating Slave APs prior to theactual joint transmission. During the joint transmission sessionnegotiation, the Master AP and Slave APs exchange information about theTarget STAs involved in the joint transmission. The Master AP and SlaveAPs also specify the joint transmission parameters that are expected tobe used throughout the session, for example the channel to be used, thePPDU format (HT, VHT or HE etc.), pre-coding schemes for MU-MIMO etc.Each joint transmission session is identified by a unique Session ID.The Master AP initiates the setup of a joint transmission session bytransmitting an AP Coordination Session Request frame to a Slave AP. Ifthe Slave AP accepts the request, it transmits back an AP CoordinationSession Response frame, with the Status code field set to Accept, to theMaster AP. The Master AP repeats the process for each Slave APparticipating in the joint transmission. To terminate a session, theMaster AP transmits the AP Coordination Session Teardown frame to aSlave AP.

FIG. 10 shows AP Coordination Action frames exchanged between the AP tonegotiate or to teardown joint transmission sessions in accordance withan example embodiment. The figure shows an AP Coordination SessionRequest 1000, an AP Coordination Session Response 1002, an APCoordination Session Teardown 1004, a table 1010 with AP CoordinationSession Action field values, and a table 1020 with AP Coordination Typefield values.

A new category of Action frames is defined for Multi-AP Coordination andindicated in the category field. Five new Action frames are defined forthe purpose of AP to AP communication related to Multi-AP Coordination,out of which three are used for setup/teardown of sessions (indicated bythe value of the “AP Coordination Session Action” field as listed intable 1010). Sessions may be setup for various types of multi-APcoordination schemes and is indicated by the value of the “APCoordination Type” field in the AP Coordination Session Request frame aslisted in table 1020. For example, for joint transmission sessions, itis set to 2. The “Target STA information” field in the AP CoordinationSession Request frame 1000 lists the MAC Addresses of one or more TargetSTAs that are expected to participate in the joint transmission.

The “Type Specific parameters” field in the AP Coordination SessionRequest frame 1000 carries additional session parameters that arespecific to the AP Coordination Type. For example, for JointTransmission, the field may specify the Channel information for thejoint transmission. The channel information may be present when theMaster AP and Slave APs are operating on different fronthaul channels.The “Type Specific parameters” field may also indicate the start time atwhich the joint transmission is expected to start. In dense networks itis common for neighboring APs to operate on different channels tomitigate inter-BSS interference. If the channel specified in the Channelinformation is different from a Slave AP's operating channel and if theSlave AP accepts the AP Coordination session request, the Slave AP isexpected to switch channel to the specified joint transmission channelbefore the indicated joint transmission start time.

As another example, for Joint Transmission, if encryption is enabled forjoint transmission, and encryption is to be performed locally at eachAP, the “Type Specific parameters” field may also include the securitykey (e.g. PTK) to be used for the encryption.

As yet another example, for Joint Transmission, the “Type Specificparameters” field may also include the amount of buffer space requestedby Master AP to be allocated by Slave APs to save JT Data frames.

FIG. 11 shows a frame 1100 in which an Ethernet Frame encapsulates JTData as well AP Coordination Action frames in accordance with an exampleembodiment.

The Master AP encapsulates the Joint Transmission Data frame (entireS-MPDU or A-MPDU carrying the Joint Transmission Data payload) within an802.3 (Ethernet) frame and transmits to the slave APs over the Ethernetlink. If encryption is to be used, the encrypted frame/s areencapsulated.

When Ethernet frames are used to exchange AP Coordination informationbetween APs, Ethertype 89-0d frames may also be used to encapsulate theAP Coordination Action frames, for example to setup or teardown a APCoordination session. In this case, the Payload Type field is set to “APCoordination” and the Ethertype 89-0d frame payload carries APCoordination Action frames. The “AP Coordination Packet Type” field inthis case is set to AP Coordination Action frames (set to 3 as indicatedin Table 620 in FIG. 6) and the Packet Content field carries the APCoordination Action frames, while the other fields in the payload areomitted.

The Destination Address in the MAC Header ensures that Slave APs do notforward the received JT Data frames to Target STAs immediately. Forexample, the sub-field is set to the Slave AP's MAC address and not tothe Target STA's MAC address.

The transmissions to different Slave APs may not be synchronized in timein wired or mixed backhaul scenario and may happen at the same time orat different times. The JT Packet ID is used to synchronize the JointTransmission content.

FIG. 12 shows a Trigger frame 1200 for Joint Transmission to a TargetSTA in accordance with an example embodiment.

The Joint Transmission Trigger frame 1200 includes the AP CoordinationSession ID 1210. The session ID is included in the JT Trigger frame toindicate which joint transmission session is being triggered. Based onthe session ID, the slave APs receiving the JT Trigger frame retrievesthe common parameters that were negotiated during the session setup.Such pre-negotiated parameters are omitted in the JT Trigger frameunless the Master AP explicitly overrides any of the parameters.Overhead of joint transmission control signaling over the wirelessmedium is reduced.

Further, the field MAC Address of Slave APs can be skipped if all SlaveAPs corresponding to a Session ID are involved in the JointTransmission. The Destination MAC Address field may also be skipped ifthe Target STA is obvious from the Session ID.

FIG. 13 shows a communication exchange 1300 in which the Master AP doesnot participate in the Joint Transmission in accordance with an exampleembodiment.

As mentioned earlier, in some cases, the Master AP may not be involvedin the actual joint transmission phase, only the Slave APs mayparticipate in the joint transmission. This may happen when the MasterAP is implemented as a central controller and is far from the TargetSTA, or the Master AP may not even be an actual AP and may be a Multi-APcontroller device in the core network. In this case, the Target STA isassociated with one of the Slave APs and not the Master AP.Communications between the Slave APs and Master AP, including the JTTrigger frame, may happen over the wired backhaul (e.g. Ethernet). Whenthere is no wireless link between the Master AP and the Slave APs, eventhe JT Trigger frames are encapsulated within Ethernet frames. Due tothe stringent time synchronization requirement for joint transmissionand because of the fact that JT Trigger frames are used for timesynchronization among the Slave APs, use of the wired backhaul fortransmission of JT Trigger frames is possible only when it can beguaranteed that all the participating Slave APs receive the JT Triggerframe at the same time. In this case, the Payload Type field is set to“AP Coordination” and the Ethertype 89-0d frame payload carries JTTrigger frames. The “AP Coordination Packet Type” field in this case isset to JT Trigger frame (set to 4 as indicated in Table 620 in FIG. 6)and the Packet Content field carries the JT Trigger frame, while theother fields in the payload are omitted. This kind of deployment removesthe constraint of requiring the Slave APs to be in wireless range of theMaster AP and enables joint transmission on a much larger scale, where aMaster AP in a centralized location can remotely manage jointtransmission in multiple physical locations. However if it cannot beguaranteed that all the participating Slave APs receive the JT Triggerframe at the same time, the JT Trigger frame is transmitted over thewireless medium.

In such cases where a Target STA is not associated with the Master AP,the Master AP may not know the value to be used for the Sequence Controlfield, or the CCMP Packet Number (PN) which are locally generated by theSlave AP. For example if the Target STA is associated with Slave AP1,prior to the data distribution phase 1320, the Master AP initiates theInfo query phase 1310 and queries the Slave AP1 for the next SequenceControl to be used, and optionally the CCMP Packet Number (PN) andencryption Key ID to be used for transmission to the Target STA. TheMaster AP uses the queried information to set the respective fields ofthe encapsulated JT Data if entire MPDUs are distributed to the SlaveAPs, or the information is distributed to the Slave APs if MPDUs forjoint transmission are locally generated by the Slave APs.

At some point prior to the data distribution phase 1320, the Master APalso makes arrangements for the upper layer data to be routed throughitself instead of through the Slave AP1. This may be done by temporarilyupdating the routing table of the network router device forwarding thedata payload to the APs such that the Master AP is recorded as theserving AP for the Target STA.

During the data distribution phase 1320, the Master AP sets the MACheader fields of the encapsulated JT Data such that the data appears tobe generated by the Slave AP1 with which the Target STA is associated,e.g. the Address 2 (TA) field of the jointly transmitted MPDUs is set tothe MAC address of the Slave AP1. Also, the sequence number subfield inthe sequence control field of the MPDUs (of the JT Data) are used asimplicit JT Identifiers, so explicit JT Packet IDs are not assigned tothe JT Data. During the Joint Transmission phase 1330, the Master APstill initiates a joint transmission by transmitting the JT Triggerframe, however only the Slave APs participate in the actual jointtransmission. For the Target STA, the transmission appears to beinitiated by the Slave AP1.

FIG. 14 shows Action Frames 1400 used by AP in the information queryphase to gather information from another AP in accordance with anexample embodiment.

The AP Coordination Info Request frame includes the RequestedInformation bitmap that indicates the information about the Slave APsparameters for a Target STA that are solicited by the Master AP. TheSlave AP uses the AP Coordination Info Response frame to report thesolicited information to the Master AP, the included information beingindicated by the Reported Information bitmap

Although the Master AP can initiate the request, it is also possible forSlave APs to initiate the request. The AP Coordination Info Requestframe 1410 includes the Requested Information bitmap that indicates theinformation about the receiving AP's parameters for a Target STA thatare solicited by the transmitting AP. The recipient AP uses the APCoordination Info Response frame 1420 to report the solicitedinformation to the soliciting AP, the included information fields beingindicated by the Reported Information bitmap. If a bit is set to 1 inthe Reported Information bitmap, the corresponding field is included inthe AP Coordination Info Response frame 1420, otherwise it is notpresent.

FIG. 15 shows a frame 1500 for data sharing from the Master AP to SlaveAPs in accordance with an example embodiment.

Instead of encapsulating the whole MAC layer frame (MPDU or A-MPDU),Master AP only encapsulates the upper layer data payload (also known asMSDU (MAC Service Data Unit)), and the other relevant fields of the MACheader within the Payload field of the Ethertype 89-0d frame body. Ifmultiple data payloads are included, the sequence control field, and theCCMP header (if included) carry the starting Sequence Number (SN) andPacket Number (PN) respectively. Based on this, each Slave AP generatesthe MPDUs or A-MPDUs to be jointly transmitted. If required, encryptionof data is performed by each Slave AP.

Copies of the Frame control, Duration/ID, QoS Control and HT Controlfields are used by Slave APs to create MAC Headers for the locallygenerated MPDUs. Alternatively, some or all of these fields may also bedistributed during JT Session setup if these fields remain the samethroughout the JT session.

The CCMP Header field 1510 is present if the “Protected Frame” bit inthe Frame Control field 1520 is set. The CCMP Header field 1510 carriesthe Packet Number (PN) to be used to encrypt the first MPDU with thesubsequent MPDUs using sequentially increasing PN.

The Sequence Control field 1520 carries the Sequence Number (SN) to beused for locally created A-MPDUs. This is used as the starting SN forthe first MPDU and increases sequentially for subsequent MPDUs in theA-MPDU.

The Packet Content field 1530 only carries higher layer payload (alsoknown as MSDU). Each of the Slave APs append the locally generated MACheaders to the higher layer payload to generate the MPDUs for jointtransmission.

FIG. 16 shows a JT Data frame 1600 as an Aggregated MAC Protocol DataUnit (A-MPDU) in accordance with an example embodiment.

Each Slave AP generates the Joint Transmission Data frame 1600 locallyand saves it in memory. For example, each Slave AP generates the MPDUsor A-MPDUs to be jointly transmitted based on the information 1602received from the Master AP. Arrows in FIG. 16 means fields are simplycopied over to the locally generated MPDUs, except some field thatrequire additions. The first generated MPDU directly uses the SequenceControl field received from the Master AP, while each subsequent MPDUwill increment the sequence number subfield within the Sequence controlfield 1620 by one. The MPDUs, or A-MPDUs may be generated right uponreception of the encapsulated data from the Master AP and saved inmemory. If encryption is required (indicated by the “Protected Frame”bit in the Frame Control field 1610), each Slave AP also encrypts thedata payload and generates and appends the MIC to the payload. The firstencrypted MPDU directly uses the CCMP Header field received from theMaster AP, while each subsequent MPDU will increment the PN subfieldwithin the CCMP Header field by one. The encrypted MPDUs are saved inmemory, indexed by the JT Packet ID 1630.

Alternatively, if the Slave APs have fast enough processors, during thedata distribution phase, the received MAC parameters and payloads aresaved in memory and the MPDU generation (and encryption if required) maybe done only after JT Trigger frame is received.

In FIG. 16, the Address 2 (TA) field 1622 in the MPDUs of the locallycreated JT Data frame 1600 is also copied from the corresponding Address2 (TA) field 1630 in the information 1602 received from the Master AP.The Address 2 (TA) field 1630 either set to the Master AP's MAC addressor to one of the Slave APs MAC Address depending on the AP with whichthe Target STA is associated. The rest of the fields of each A-MPDUsubframe (MPDU delimiter, Padding, FCS, etc.) as well as the EOF paddingare locally generated. Further, in the CCMP Encryption frame, the CCMPencryption is performed by the Slave AP if the “Protected Frame” bit inthe Frame Control field 1610 is set.

One benefit of the frame 1600 is that the overhead of data transfer overthe backhaul is reduced.

FIG. 17 shows a frame 1700 as an Aggregated MAC Protocol Data Unit(A-MPDU) used for data sharing to Slave APs in accordance with anexample embodiment.

The Master AP uses the 802.11 Data frames 1700 with 4 Address MAC Headerformat to distribute JT Data to Slave APs (without using Ethertype 89-0dencapsulation). This distribution scheme may be used when the Slave APsare associated with the Master AP, for example in Wi-Fi EasyMeshdeployments.

Upon receiving Joint Transmission Data from the Master AP, the Slave APgenerates the MPDUs to be jointly transmitted. The Sequence Numberwithin the Sequence Control fields 1734 in the MAC header of thegenerated MPDUs 1730 are used as implicit JT Identifiers.

Consider an example of deployments where the Target STA is associatedwith the Master AP and the Master AP also participates in the actualjoint transmissions. The Master AP transmit the A-MDPU 1700 to the SlaveAP to distribute the JT data. Each Data frame within the MPDUs of theA-MPDU uses the four address MAC Header format and the Frame Body of theMPDU 1710 carries the actual Data payload 1720 (encrypted if requiredand including the CCMP Header field and the MIC field) to be jointlytransmitted. In this case the JT Data refers to the Data payload 1720(encrypted if required and including the CCMP Header field and the MICfield). Since the final destination of the Data payload 1720 is not theSlave AP, the “To DS” and the “From DS” bits in the Frame Control field1712 are both set to 1 to differentiate from AP to STA or STA to APtransmissions. The HE Control field 1714 is also enhanced for EHT usageand a new Control ID is defined for AP Coordination. The Control fieldmay be used to carry control signals for various multi-AP Coordinationschemes, the AP Coordination Type 1716 indicating the Coordinationscheme and may be set to one of the values in Table 1020 in FIG. 10, forexample to 2 for Joint Transmission in which case the subsequent fieldof the HE Control field is used to carry the JT Sequence Control 1718.The JT Sequence Control field 1718 carries the Sequence Control field1734 of the actual MPDU to be jointly transmitted.

Upon receiving the A-MPDU 1710 from the Master AP that carries the HEControl field 1714 for AP Coordination, the addressed Slave AP (that isindicated by the Address 1 (RA)), instead of forwarding the A-MPDU tothe Target STA (indicted by the Address 3 (DA)), generates the MPDUs orA-MPDUs to be jointly transmitted based on the information received fromthe Master AP. The generated MPDUs 1730 are 802.11 Data frames that usethe three address MAC Header format.

In FIG. 17, the arrows signify fields are copied over from the receivedMPDUs to the generated MPDUs, except that in the generated MPDUs, the“To DS” bit in the Frame Control field 1732 is set to 0 while the “FromDS” bit is set to 1. The Sequence Control field 1734 of the generatedMPDU is copied over from the JT Sequence Control 1718 received from theMaster AP. The Duration field, the Address 2 (TA) field and the QoSControl field are copied without any modification, while the Address 3(DA) field is copied over to the Address 1 (RA) field and the Address 4(SA) field is copied over to Address 3 (SA) field in the generatedMPDUs. The HE Control field carrying the JT Sequence Control field isomitted in the generated MPDU. The frame body of the generated MPDU isdirectly copied over from the MPDU 1710 as received from the Master AP(i.e. without any further processing). The FCS field 1738 however isgenerated locally by the Slave APs. An important aspect to note here ifthe Data Payload 1720 is encrypted, is that the CCMP encryption isperformed for the consumption of the Target STA and hence the MAC headerparameters used for the encryption is based on the MAC header fieldsthat are included in the actual MPDU 1730 that are jointly transmittedand not based on the MAC header fields of the MPDU 1710. Specifically,during the CCMP encapsulation procedure, the Master AP uses the FrameControl field 1732, Address 1 (RA) field 1740, Address 2 (TA) field1742, Address 3 (SA) field 1744, the Sequence Control field 1746 and theQoS Control field 1748 as would be generated by the Slave APs toconstruct the additional authentication data (AAD) to be used for theCCMP encryption. The Address 4 field is not included in the AAD. TheCCMP Header field, the encrypted data payload 1720 and the generated MICare included in the frame body of MPDU 1710 and are directly copied overto the frame body of MPDU 1730 by the Slave APs without furtherprocessing. This significantly reduces the processing overhead relatedto encryption for Slave APs.

The MPDUs, or A-MPDUs may be generated by the Slave APs right uponreception of the data from the Master AP and saved in memory. The MPDUsare saved in memory indexed by the Sequence Number subfield of theSequence Control field 1734. Alternatively, if the Slave APs have fastenough processors, during the data distribution phase, the receivedMPDUs/A-MPDUs are saved in memory without any modification and the MPDUgeneration (for joint transmission) may be done only after JT Triggerframe is received.

FIG. 18 shows a Joint Transmission Trigger frame 1800 in accordance withan example embodiment.

The JT Trigger frame includes a list of Sequence Number of MPDUs to bejointly transmitted. Slave APs construct the A-MPDU from the saved MPDUsif required.

The sequence number subfield in the sequence control field of the MPDUs(JT Data), for example 1620 in FIG. 16 or 1732 in FIG. 17, are used asimplicit JT Identifier. This allows the Master AP more flexibility inchoosing the content of the JT Data during the actual joint transmission(by indicating specific sequence numbers in the Sequence NumberInformation field 1810 in the JT Trigger frame 1800).

This flexibility can be executed, for example, during jointre-transmissions in which only the failed MPDUs are re-transmitted. TheSequence Number Information field 1810 identifies the MPDUs to bejointly transmitted. The bits set to 1 in the Sequence Number Bitmapsubfield indicates the sequence number of the MPDUs to be included, withthe first bit (n=1) in the bitmap corresponding to the Starting SequenceNumber (SSN) subfield and the nth bit corresponding to (SSN+n−1).

FIG. 19 is example of Distributed MU-MIMO Joint Transmission 1900 to twoSTAs that are both associated with the Master AP in accordance with anexample embodiment.

Numbers 1910 and 1912 show data distribution to the Slave APs. JT Dataare distributed to Slave APs that are destined for STA1 and STA2respectively. For example the JT Data 1910 and 1912 may be A-MPDU 1700in FIG. 17. Upon receiving the JT Data 1910 and 1920, the Slave APs maygenerate the MPDUs 1730 for joint transmission by copying over thenecessary fields from the received JT Data. The Slave APs may furtheraggregate the locally generated MPDUs into a single A-MPDU and save theA-MPDU in the designated local buffer. Number 1914 shows the JointTransmission Trigger frame used to initiate the joint transmission toTarget STAs. The JT Trigger frame 1914 initiates the MU jointtransmission that uses two Spatial Streams. Number 1920 shows Jointtransmission to STA1: S.N 1-5 to STA1 using Spatial Stream 1. Number1922 shows Joint transmission to STA2: S.N 11-15 to STA2 using SpatialStream 2. 1920 and 1922 take place at the same time but use differentspatial streams.

FIG. 20 is an example of an electronic device 2000 in accordance with anexample embodiment.

The electronic device 2000 includes a power source 2010, memory 2020,central processing unit (CPU) 2030, secondary storage 2040, and wirelessI/F 2050 (including a transmitter and/or receiver). The wireless I/F2050 includes a MAC 2052 and PHY 2060 in communication with an antenna2070. The MAC 2052 further includes a JT Identity generator 2054, JTData Buffer 2056, and a JT Data encapsulation/de-encapsulation 2058.

Consider an example embodiment in which the electronic device 2000 is anAP, such as a Master AP or Slave AP (noting that the JT Identitygenerator 2054 is only present in Master AP).

The electronic device 2000 includes circuitry that operates to generatea frame that includes the JT data and a JT identity that uniquelyidentifies the JT data. For example, the JT Identity generator block2054 is responsible for generating the JT identity corresponding to theJT Data distributed to the Slave APs. The JT Dataencapsulation/de-encapsulation block 2058 is used by the Master AP toencapsulation the JT Data within an 802.11 Data frame or an 802.3Ethernet frame during data distribution phase. The block is used by theSlave AP to de-encapsulate the JT Data received from Master AP. The JTData Buffer 2056 stores the JT Data used for joint transmission. In theMaster AP, this may not be a separate buffer but may be a sharedbuffered that stores all outgoing data frames. In the Slave AP, this maybe a separate buffer used exclusively to store data frames to be usedfor joint transmissions. The electronic device 2000 further includescircuitry, such as a wireless transmitter and/or antenna 2070, thatenable the APs to transmit the data frames to one or more communicationapparatus, such as to one or more STAs in a wireless network.

The present disclosure can be realized by software, hardware, orsoftware in cooperation with hardware. Each functional block used in thedescription of each embodiment described above can be partly or entirelyrealized by an LSI such as an integrated circuit, and each processdescribed in each embodiment may be controlled partly or entirely by thesame LSI or a combination of LSIs. The LSI may be individually formed aschips, or one chip may be formed so as to include a part or all of thefunctional blocks. The LSI may include a data input and output coupledthereto. The LSI here may be referred to as an IC, a system LSI, a superLSI, or an ultra LSI depending on a difference in the degree ofintegration. However, the technique of implementing an integratedcircuit is not limited to the LSI and may be realized by using adedicated circuit, a general-purpose processor, or a special-purposeprocessor. In addition, a FPGA (Field Programmable Gate Array) that canbe programmed after the manufacture of the LSI or a reconfigurableprocessor in which the connections and the settings of circuit cellsdisposed inside the LSI can be reconfigured may be used. The presentdisclosure can be realized as digital processing or analogue processing.If future integrated circuit technology replaces LSIs as a result of theadvancement of semiconductor technology or other derivative technology,the functional blocks could be integrated using the future integratedcircuit technology. Biotechnology can also be applied.

The present disclosure can be realized by any kind of apparatus, deviceor system having a function of communication, which is referred to as acommunication apparatus.

The communication apparatus may comprise a transceiver andprocessing/control circuitry. The transceiver may comprise and/orfunction as a receiver and a transmitter. The transceiver, as thetransmitter and receiver, may include an RF (radio frequency) moduleincluding amplifiers, RF modulators/demodulators and the like, and oneor more antennas.

Some non-limiting examples of such a communication apparatus include aphone (e.g, cellular (cell) phone, smart phone), a tablet, a personalcomputer (PC) (e.g, laptop, desktop, netbook), a camera (e.g, digitalstill/video camera), a digital player (digital audio/video player), awearable device (e.g, wearable camera, smart watch, tracking device), agame console, a digital book reader, a telehealth/telemedicine (remotehealth and medicine) device, and a vehicle providing communicationfunctionality (e.g., automotive, airplane, ship), and variouscombinations thereof.

The communication apparatus is not limited to be portable or movable,and may also include any kind of apparatus, device or system beingnon-portable or stationary, such as a smart home device (e.g, anappliance, lighting, smart meter, control panel), a vending machine, andany other “things” in a network of an “Internet of Things (IoT)”.

The communication may include exchanging data through, for example, acellular system, a wireless LAN system, a satellite system, etc., andvarious combinations thereof.

The communication apparatus may comprise a device such as a controlleror a sensor which is coupled to a communication device performing afunction of communication described in the present disclosure. Forexample, the communication apparatus may comprise a controller or asensor that generates control signals or data signals which are used bya communication device performing a communication function of thecommunication apparatus.

The communication apparatus also may include an infrastructure facility,such as a base station, an access point, and any other apparatus, deviceor system that communicates with or controls apparatuses such as thosein the above non-limiting examples.

It will be understood that while some properties of the variousembodiments have been described with reference to a device,corresponding properties also apply to the methods of variousembodiments, and vice versa.

It will be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments without departing from the spirit orscope of the disclosure as broadly described. The present embodimentsare, therefore, to be considered in all respects illustrative and notrestrictive.

Other example embodiments include but are not limited to the followingexamples.

One example embodiment is an access point (AP) comprising: circuitry,which, in operation, generates a frame, a frame body of the frameincludes joint transmission (JT) data and a JT identity that uniquelyidentifies the JT data; and a transmitter, which, in operation,transmits the frame to one or more APs that jointly transmit the JT datato a communication apparatus.

With the access point, the circuitry, in operation, generates a JTtrigger frame that includes the JT identity of the JT data, and thetransmitter in operation, transmit the JT trigger frame to the one ormore APs.

With the access point, the JT trigger frame includes a MAC address ofthe communication apparatus.

With the access point, the JT data is carried as a payload of anEthertype 89-0d frame body.

With the access point, the frame is one of an IEEE 802.11 data frame andan Ethernet frame.

With the access point, the JT data is one or more MAC Protocol DataUnits (MPDU) addressed to the communication apparatus.

With the access point, the JT identity is one of a uniquely assigned JTpacket ID, a value of a Sequence Number subfield within a SequenceControl field of an encapsulating IEEE 802.11 data frame, and value of aSequence Number subfield within a Sequence Control field of a MPDUwithin a JT Data.

With the access point, JT data has higher layer payload and commonfields required by the receiving APs to locally construct one or moreMAC Protocol Data Units (MPDU) jointly transmitted to the communicationapparatus.

With the access point, the JT data is carried as a payload of an IEEE802.11 Data frame using a four address MAC header format; a MAC headerof the IEEE 802.11 Data frame includes a control field that indicates aSequence Control field of the IEEE 802.11 Data frame to be jointlytransmitted; and the JT identifier includes a value of a Sequence Numbersubfield within the Sequence Control field.

With the access point, the access point negotiates an AP Coordinationsession with the one or more APs, the AP Coordination session specifiesan AP coordination scheme as Joint Transmission, and the AP Coordinationsession is identified by a session ID.

With the access point, the access point transmits a PHY Protocol DataUnit (PPDU) constructed from the JT data after a fixed duration from anend of a JT Trigger frame.

Another example embodiment is an access point (AP) that comprises areceiver, which, in operation, receives from an AP a frame that includesJoint Transmission (JT) data and a JT identity that uniquely identifiesthe JT data; and local memory that stores the JT data and the JTidentity.

With the access point, the receiver further operates to receive from theAP a JT Trigger frame carrying the JT identity of the JT data; theaccess point retrieves the JT data with matching JT identity from thememory and transmits a physical layer protocol data unit (PPDU)constructed from the JT data after a fixed duration from an end of theJT Trigger frame.

Another example embodiment is a communication method in which one ormore access points (APs) jointly transmit to a communication apparatus.The method comprises transmitting, from a first AP and to one or moresecond APs, a frame in which a frame body of the frame includes jointtransmission (JT) data and a JT identity that uniquely identifies the JTdata; and transmitting, from the one or more second APs, the JT datajointly to the communication apparatus.

The method further comprises synchronizing PHY and MAC parameters at twoor more transmitting APs such that the transmission signals received bya communication apparatus from the two or more transmitting APs areexactly the same.

What is claimed is:
 1. An access point (AP) comprising: circuitry,which, in operation, generates a frame including joint transmission (JT)data and a JT identity that uniquely identifies the JT data; and atransmitter, which, in operation, transmits the frame to one or moreother APs that jointly transmit the JT data to a communicationapparatus.
 2. The access point of claim 1, wherein the circuitry, inoperation, generates a JT trigger frame that includes the JT identity ofthe JT data, and the transmitter in operation, transmit the JT triggerframe to the one or more other APs.
 3. The access point of claim 2,wherein the JT trigger frame includes a MAC address of the communicationapparatus.
 4. The access point of claim 1, wherein the JT data iscarried as a payload of an Ethertype 89-0d frame body.
 5. The accesspoint of claim 1, wherein the frame is one of an IEEE 802.11 data frameand an Ethernet frame.
 6. The access point of claim 1, wherein the JTdata is one or more MAC Protocol Data Units (MPDU) addressed to thecommunication apparatus.
 7. The access point of claim 1, wherein the JTidentity is one of a uniquely assigned JT packet ID, a value of aSequence Number subfield within a Sequence Control field of anencapsulating IEEE 802.11 data frame, and value of a Sequence Numbersubfield within a Sequence Control field of a MPDU within a JT Data. 8.The access point of claim 1, wherein JT data has higher layer payloadand common fields required by the receiving APs to locally construct oneor more MAC Protocol Data Units (MPDU) jointly transmitted to thecommunication apparatus.
 9. The access point of claim 1, wherein the JTdata is carried as a payload of an IEEE 802.11 Data frame using a fouraddress MAC header format; a MAC header of the IEEE 802.11 Data frameincludes a control field that indicates a Sequence Control field of theIEEE 802.11 Data frame to be jointly transmitted; and the JT identifierincludes a value of a Sequence Number subfield within the SequenceControl field.
 10. The access point of claim 1, wherein the access pointnegotiates an AP Coordination session with the one or more other APs,the AP Coordination session specifies an AP coordination scheme as JointTransmission, and the AP Coordination session is identified by a sessionID.
 11. The access point of claim 1, wherein the access point transmitsa PHY Protocol Data Unit (PPDU) constructed from the JT data after afixed duration from an end of a JT Trigger frame.
 12. An access point(AP), comprising: a receiver, which, in operation, receives from anotherAP a frame that includes Joint Transmission (JT) data and a JT identitythat uniquely identifies the JT data; and local memory that stores theJT data and the JT identity.
 13. The access point of claim 12, whereinthe receiver further operates to receive from the other AP a JT Triggerframe carrying the JT identity of the JT data; the access pointretrieves the JT data with matching JT identity from the memory andtransmits a physical layer protocol data unit (PPDU) constructed fromthe JT data after a fixed duration from an end of the JT Trigger frame.14. A communication method comprising: generating, at a first accesspoint (AP), a frame including joint transmission (JT) data and a JTidentity that uniquely identifies the JT data; and transmitting, fromthe first AP, the frame to one or more second APs that jointly transmitthe JT data to a communication apparatus.
 15. A communication methodcomprising: receiving, at one or more access points (APs), a frame thatis transmitted from another AP and that includes Joint Transmission (JT)data and a JT identity that uniquely identifies the JT data; and storingthe JT data and the JT identity in local memory.
 16. The communicationmethod according to claim 15 further comprising: transmitting, from theone or more APs, the JT data jointly to a communication apparatus. 17.The communication method according to claim 14 further comprising:synchronizing PHY and MAC parameters at the more APs such that the JTdata received by the communication apparatus from the more APs areexactly the same.